Hip-hop and R&B's brightest were only sometimes at their best at last night's Summer Jam at MCI Center. A promotional event for WKYS-FM, the show tried to pack nine of R&B radio's top acts into a three-hour show. What resulted was an uneven yet still entertaining night of disappointment, showmanship and surprise.

Shortly after the show began, audience members were informed that DMX, one of hip-hop's most idolized figures, had been arrested earlier in the day and would be unable to attend. Fortunately, popular drive-time radio jock EZ Street was able to calm the near riotous swell of disappointment by offering attendees their choice of refunds or free tickets to the next local DMX show. Last night's concert was not without DMX's influence, though. Drag-On, a member of DMX's popular Ruff Ryders clique, put on a crowd-pleasing set of songs from their hit compilation "Ryde or Die, Vol. 1," which recently entered Billboard's pop album's chart at No. 1. Concertgoers also learned that Missy "Misdemeanor" Elliott would not be performing. According to sources at her label, Elektra, Elliott canceled the appearance much earlier, even though she was still featured in the radio station's advertising yesterday. Elliott's no-show was especially disappointing in light of her lively performance on David Letterman's "Late Show" just days earlier.

The Summer Jam opened with a sexy and energetic set by the female R&B foursome Destiny's Child that included their debut smash "No No No" and several cuts from their playful and surprisingly confident new album, "The Writings on the Wall," thus far one of the year's best R&B releases. Wearing red bandanna tops and skintight blue denim jeans, the group roused the crowd with their current single, "Bills, Bills, Bills." In the chorus to "Bills," which was written and produced by the folks behind TLC's controversial critique of "broke" suitors, "No Scrubs," Destiny's Child asks: "Can you pay my bills/ Can you pay my telephone bills/ Can you pay my automo-bills?"

Another winning performance came from hip-hop veterans Naughty by Nature, the perfect Summer Jam act since they're known for such summer jams as "O.P.P.," "Hip Hop Hooray" and "Feel Me Flow." Their new single for this summer is even called "Jamboree." Lead rapper Treach was plagued by mike problems but displayed no lack of virility and verve as he bounded across the stage delivering his arsenal of hip-hop anthems.

New Orleans rap star and entrepreneur Master P., who seems to be engaged in a full-scale D.C. outreach effort with recent record store appearances and radio interviews, dropped by to introduce a few of the night's acts. There was hardly a person seated when he first took the stage. And although he never actually performed, he at least gave the crowd some sage advice against getting "rowdy rowdy" after the show.

Other appearances included rappers J.T. Money, who had a Top 10 pop hit with "Who Dat," and Krayzie Bone, a member of Bone Thugs-N-Harmony, who strangely seemed to be lip-syncing his trademark rapid-fire rhymes. Soulman wannabe Case also performed, but sadly he hasn't improved as a live vocalist since he played Constitution Hall with Dru Hill a few months ago.

Similarly, Nas, one of hip-hop's most acclaimed lyricists, again proved that he's better in the studio recording booth than live on stage, where he paces back and forth so much that it's almost dizzying. Muddled sound drowned the musical subtleties in songs like "It Ain't Hard to Tell." And his current hit "Hate Me Now" almost misfired when the backing track initially failed to start. The song got the crowd on its feet again, but by then it was almost time to leave anyway.

Still, despite the last-minute cancellations and frequent technical glitches, the show lived up to its name. It took place in the summer. And more often than not, it jammed.

CAPTION: Naughty by Nature's Treach was full of energy at the WKYS Summer Jam.